[PATCH v2 kvmtool 0/2] Add libfdt library

[Alexandru Elisei]

I found it very difficult to cross-build kvmtool for all arches because for
some architectures I couldn't get libfdt to install: either dtc wasn't
compiling (x86 machine, Arch Linux, missing yaml.h include when building
for arm and powerpc), or libfdt was not being found by Makefile after
installing it (x86 machine, Debian 11, building for powerpc). It was
possible to compile only libfdt and teach Makefile where to look for it,
which is what I ended up doing, but in my opinion, that's not an ideal user
experience.

This is my attempt at making compilation easier by pulling in the libfdt
library and having kvmtool compile it when an architecture requires it. All
the user needs to do now is to find a suitable cross-compiler toolchain
with glibc included [1]*.

The static version of libfdt is linked against the final binary, regardless
if kvmtool is built as a static or dynamic binary. This only happens for
those arches that require libfdt (arm, arm64, riscv, powerpc); libfdt is
not built for MIPS and x86. This has been measured to increase the size of
the binary by 110KB, or 5.3% (details in patch #1).

I am pretty happy with how libfdt has been integrated with the kvmtool
build system. The only niggle is that the libfdt_clean target echoes the
commands to remove the build artifacts:

$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- clean
Makefile:368: Skipping optional libraries: bfd zlib aio
  CLEAN (libfdt)
rm -f libfdt/*.o libfdt/libfdt.a
rm -f libfdt/libfdt.so.1
  CLEAN

but I believe that's impossible to change without modifying the libfdt
Makefile, which I don't want to do to keep it as easy as possible to update
libfdt.

Redid the measurements about how libfdt affects the build time when
building from a clean directory (incremental builds do not rebuild libfdt):

- On a rockpro64, on the little core (Cortex-A53), running

$ time taskset -c 0 make

with libfdt it takes 90.838s (measured for one build, very similar to the
previous measurements); without libfdt it takes 84.263s (measured as
above). That's a 6.575s absolute increase, or a 7.803% relative
increase.

- On the same rockpro64, on the big core (Cortex-A72), running

$ time taskset -c 5 make

with libfdt takes 45.178s (one build, very similar to the measurements for
v1); without libfdt it takes 41.919s (measured as above).  That's a 3.260s
absolute increase, or a 7.777% relative increase.

I believe that the ease of use more than justifies the increased
compilation time.

*only for x86 hosts.

Testing
=======

On x86 host, compiled for x86, MIPS, arm, arm64, powerpc, riscv. Booted an
x86 VM.

On arm64 host, compiled for arm64 and arm. I tried to cross-compile for
other targets, but I couldn't find a cross-compiler toolchain for arm64
hosts that included a libc implementation. The arm cross-compiler was
downloaded from the developer.arm.com [2]. Ran kvm-unit-tests for arm64 and
arm (on the arm64 version of kvmtool), and also booted a kernel.

Changelog
=========

Changes since v1:

- Always link kvmtool against the static version of libfdt. The dynamic
  lkvm binary was rather embarrassingly for me still using the system
  library (Andre).

[1] https://toolchains.bootlin.com/
[2] https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/downloads

Alexandru Elisei (2):
  Add libfdt library
  INSTALL: Remove all mentions of libfdt

 INSTALL                  |   27 +-
 Makefile                 |   39 +-
 libfdt/.gitignore        |    1 +
 libfdt/Makefile.libfdt   |   18 +
 libfdt/TODO              |    3 +
 libfdt/fdt.c             |  335 ++++++
 libfdt/fdt.h             |   66 ++
 libfdt/fdt_addresses.c   |  101 ++
 libfdt/fdt_check.c       |   93 ++
 libfdt/fdt_empty_tree.c  |   38 +
 libfdt/fdt_overlay.c     |  867 +++++++++++++++
 libfdt/fdt_ro.c          |  859 +++++++++++++++
 libfdt/fdt_rw.c          |  500 +++++++++
 libfdt/fdt_strerror.c    |   60 ++
 libfdt/fdt_sw.c          |  384 +++++++
 libfdt/fdt_wip.c         |   94 ++
 libfdt/libfdt.h          | 2147 ++++++++++++++++++++++++++++++++++++++
 libfdt/libfdt_env.h      |   96 ++
 libfdt/libfdt_internal.h |  192 ++++
 libfdt/meson.build       |   55 +
 libfdt/version.lds       |   83 ++
 21 files changed, 6018 insertions(+), 40 deletions(-)
 create mode 100644 libfdt/.gitignore
 create mode 100644 libfdt/Makefile.libfdt
 create mode 100644 libfdt/TODO
 create mode 100644 libfdt/fdt.c
 create mode 100644 libfdt/fdt.h
 create mode 100644 libfdt/fdt_addresses.c
 create mode 100644 libfdt/fdt_check.c
 create mode 100644 libfdt/fdt_empty_tree.c
 create mode 100644 libfdt/fdt_overlay.c
 create mode 100644 libfdt/fdt_ro.c
 create mode 100644 libfdt/fdt_rw.c
 create mode 100644 libfdt/fdt_strerror.c
 create mode 100644 libfdt/fdt_sw.c
 create mode 100644 libfdt/fdt_wip.c
 create mode 100644 libfdt/libfdt.h
 create mode 100644 libfdt/libfdt_env.h
 create mode 100644 libfdt/libfdt_internal.h
 create mode 100644 libfdt/meson.build
 create mode 100644 libfdt/version.lds

-- 
2.36.1